Gastric and tracheal aspirates from healthy newborn infants and infants with repiratory distress syndrome (RDS) will be analyzed for content of lecithin, lecithin:sphingomyelin ratio and lecithin fatty acid content to evaluate the relative importance of quantity and quality of surfactant lecithin in the development of RDS. Sequential studies of these parameters in infants with RDS will be carried out to determine whether return of one or other of these parameters will be helpful in predicting when an infant may safely be weaned from a respirator. Similar studies will be performed in adult patients with "shock lung". The question of quality of lecithin in relation to surface activity will be further examined using carefully defined lecithin mixtures, as well as total lipids from lung lavage extracts. Surfactant lecithin secretion by lung slices from control and essential fatty acid (EFA) deficient rats will be studied in an in vitro system. Further studies will be directed to an examination of lung fatty acid desaturase activity in control and EFA deficient tissue and microsomes. Similarly, conversion of linoleic acid to arachidonic acid will be examined in control and EFA deficient animals. Multi-compartmental models of surfactant lecithin metabolism will be tested using data obtained in long term turnover studies with various tracers in control and EFA deficient rats.